The invention discloses a disconnection detection circuit of a multi-cell protection board. The disconnection detection circuit can separately detect the disconnection and overvoltage of the BAT<1>-BAT cells in exclusion to the highest BATn by multiplexing overvoltage comparators. The disconnection detection circuit is composed of pull-up current sources I<1>-I and overvoltage comparators OV<1>-OV, and divider resistors R01-R0n-1, and can detect overvoltage and disconnection of the n-1 cells. A time sequence and control unit generates a narrow pulse signal XCLKHV which has a certain period. The narrow pulse signal XCLKHV controls the states of switches SW<1>-SW of overvoltage and disconnection detection of respective cell. According to the invention, the disconnection detection circuit addresses the failure of traditional batteries to simultaneously detect battery disconnection and overvoltage and in presence of voltage shortage of a battery, detect disconnection. The disconnection detection circuit uses narrow pulse signals XCLKHV as signals of disconnection detection switches, which greatly reduces power consumption of circuits; and since the disconnection detection circuit only uses pull-up current and multiplexes the overvoltage comparator, which effectively reduces the area of the circuit.